Not Applicable.
Not Applicable.
1. Field of the Invention
This invention pertains generally to devices and methods for finishing the surfaces of wood and fiberboard items, and more particularly to an apparatus and method for applying decorative coating from a foil onto curvilinear and irregular-shaped edges of wood pieces without the need for a template or other guide structure.
2. Description of the Background Art
As dimensional lumber is becoming increasingly scarce and expensive, much furniture is now made from board material comprising pressed and bonded sawdust, wood chips or wood fibers, such as reconstituted fiberboard, chip board and medium density fiberboards or MDF. In its natural state, MDF and other fiberboard materials are somewhat unattractive and do not provide finished surfaces suitable for use as furniture or for decorative applications. In order to make MDF and other fiberboard look more like the dimensional lumber it replaces, it is desirable to cover the board surfaces with a decorative film which simulates a wood grain finish. This is carried out by various surface finishing treatments to improve the physical appearance of the MDF. A frequently used surface finishing treatment process is foiling, wherein a wood grain pattern or other decorative pattern is painted onto a roll of plastic carrier film or tape, and then, using heat and pressure, the decorative paint pattern is transferred from the film to the MDF surface. The foil typically comprises a carrier film such as MYLAR(copyright) polyester, a heat release adhesive adjacent to or on the carrier film, a layer of decorative paint or pigment placed on the heat release adhesive, and a heat activated adhesive on top of the decorative paint layer. When the foil is heated and pressed against a substrate such as the edge of a board, the heat activated adhesive sticks to the substrate while the heat release adhesive is released or disengages from the carrier film, thus providing for transfer of the decorative paint layer to the board from the film.
In the past, edge foiling of rectangular boards has been carried out in four separate passes by various types of machines. More recently, single pass edge foiling of all four edges of rectangular boards, as well as contoured edges of non-rectangular boards, has been achieved through use of a template which exactly matches the shape of the edges of the board which is to be foiled. The template generally has a guide structure associated with its edges, such as a chain which can be driven by a sprocket. The template pattern serves to hold the board against the foiling wheel from which the decorative foil is transferred to the board edge.
Several drawbacks are associated with conventional edge foiling devices and other surface finishing devices and methods which require templates. For example, surface finishing machines generally require that each board have its own template with a precise edge pattern that matches the board. The template patterns are costly to build, maintain and store, and use of template edge foiling devices requires that the board have exactly the same shape as the template pattern, or the foil will not be applied properly to the board edges. In order to carry out edge foiling of a different-shaped board on the foiling device, there is necessary delay because the previous template must removed from the device and a new template installed thereon which matches the edge contours of the new, different-shaped board to be finished.
Another important problem present in conventional edge foiling machines is that the boards are moved with a constant speed in relation to the chain on the template, rather than at the appropriate or optimum speed for the particular edge or peripheral contour of the board which is being foiled. This results in a peripheral speed which varies with the shape of the board edges and causes uneven application of the decorative coating from the foil onto the board edges. A certain amount of heat and pressure for a given amount of time is required for proper foiling. Conventional edge foiling machines which vary the peripheral speed of the board tend to apply heat and pressure from the foiling wheel onto the board for too much time in the straight sections of edges, and for too little time in the corners and curved sections of the edges, thus resulting in uneven application and poor adhesion of the foil to board edges.
Yet another deficiency in conventional edge surface finishing devices is that scratching or marring of previously top-finished and/or bottom finished board surfaces may occur during edge finishing due to the manner in which the machines hold the boards during the edge finishing operation.
Accordingly, there is a need for a surface finishing apparatus for MDF boards and the like which does not require the use of templates or guide structures, which can be used for edge-foiling or edge finishing of boards having irregular and curvilinear edge structures, which can consecutively carry out edge-finishing on different shaped boards without requiring exchange of templates or other machine adjustment between boards, and which does not damage previously finished top and bottom surfaces. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in conventional foiling machines.
The present invention is an apparatus and method for surface finishing boards or other workpieces of varying configurations without the use of templates. In its most general terms, the invention comprises (i) surface finishing means, (ii) drive means for rotating a workpiece and providing radial force to a workpiece in the direction of the surface finishing means, (iii) means for pushing, moving or directing the surface finishing means towards the drive means, (iv) hold-down means for holding a workpiece against the drive means and retaining the workpiece in place during surface finishing, and (v) speed follower means for controlling or adjusting the speed of the drive means according to the speed or rate of operation of the surface finishing means. The surface finishing means, drive means, hold-down means and speed follower means are all preferably associated with a base or a work platform which includes a ball-bearing or air cushion table for flat workpieces.
By way of example and not of limitation, the surface finishing means preferably comprises a foiling or foil transfer assembly having a foiling head or wheel which is rotatably driven by a DC drive or other rotational power source, a swivel-mounted oven positioned to heat the foiling head, an unwind motor for a spool of transfer foil, and tensioning means in the form of a jockey arm and roller. The foiling assembly is slidably or movably mounted on the base. A rewind arm and a uptake motor are generally included on the base for receiving spent or used foil from the foil transfer assembly. A plurality of rollers or wheels are provided to direct foil from the spool to the foiling head and to the rewind arm and uptake motor, and to control tension of the foil. Other types of paint or coating application assemblies, surface planers, sanders, buffers, polishers, or other surface finishing or surface treating means may also be utilized with the invention as alternatives to the foil transfer assembly.
The drive means for simultaneously providing rotational and radial force to a workpiece preferably comprises a pair of converging axis drive wheels or feed rollers which are rotatably mounted on the base and positioned to frictionally engage a workpiece along its bottom surface in order to rotationally and radially drive or move the workpiece. The axially convergent drive wheels are canted, tilted or otherwise leaning towards each other such that a point of convergence exists for the rotational axes of the drive wheels. In one embodiment of the drive means, the rotational axes of the drive wheels are substantially perpendicular to the plane of the board or workpiece being finished, while in a second embodiment of the drive means the rotational axes of the drive wheels are substantially parallel with the plane of the board or workpiece being finished. Both embodiments impart rotational and radial force to a workpiece due to the angled or canted relationship of the drive wheels. The drive wheels preferably have a tapered, frusto-conical structure and configuration and have traction generating surfaces for engaging a workpiece. The point of convergence of the rotational axes of the drive wheels can be adjusted by adjusting the cant or tilt of the drive wheels over an angle of arc in order to vary the amount of rotational and/or radial force applied to the workpiece. The drive wheels are preferably mounted on spindles which are mechanically interfaced with a rotational power source such as a feed drive stepper motor.
The hold-down means preferably comprises an air clamp or air bearing assembly which is designed so that a flow of air maintains pressure on the workpiece and holds the workpiece against the drive wheels without mechanical contact between the air clamp and the workpiece. One or more holes in the air clamp allow some of the air to escape axially, relative to the clamp""s movement. This air blowing against the substrate holds the air clamp slightly away from the substrate, thus protecting the delicate surface treatment of the substrate from marring. The air clamp may include a skirt to create or define a plenum to better control air flow. The air clamp position is adjustable in relation to the tapered drive disks. The hold-down means may alternatively comprise a pair of canted upper hold-down disks which are positioned opposite the drive disks of the drive means and which hold the workpiece in place against the drive disks.
The speed follower means provides for motion control of the apparatus by utilizing an indexer computer or microprocessor, a high-resolution encoder, and a multiple position range selector switch which are linked or interfaced together with the drive means and surface finishing means. The encoder is positioned to monitor rotational speed of the foiling head. The indexer is enabled by a sequence controller computer or microprocessor, for which a speed is set via the range selector switch. The range selector switch changes the value of the band width conversion ratio within a fuzzy logic algorithm tree included within an open control program associated with the indexer. The fuzzy logic algorithm tree uses a conversion ratio along with the clocked speed differential of the encoder to calculate running speed values for the surface finishing means. The running speed of operation of the surface finishing means is inversely related by the indexer to the operating speed of the drive means. Thus, when a foiling head speed exceeds a specific range, the indexer instructs the drive means to slow down.
The means for pushing or directing the surface finishing means towards the drive means preferably comprises a pneumatically actuated sliding platform. The surface finishing means is mounted on the sliding platform and is slidably moved with the sliding platform by a pneumatic cylinder relative to the base and drive means so that the surface finishing means is moved towards the workpiece by the sliding platform while the workpiece is radially forced or moved toward the surface finishing means by the drive means.
The safe operation of the apparatus comprising the present invention is ensured by the sequence controller which interfaces with the components of the surface finishing means so that the drive means, heating oven and/or other components can be turned on only when the foiling head is rotating.
An object of the invention is to provide a surface finishing apparatus which neatly and accurately carries out surface finishing of wood boards or other substrates having curvilinear, irregular and/or contoured edges.
Another object of the invention is to provide a surface finishing apparatus which can finish surfaces of various types of substrates.
Another object of the invention is to provide a surface finishing apparatus which finishes the edges of a top and/or bottom finished piece without marring or damaging the top and/or bottom finished surfaces.
Another object of the invention is to provide a surface finishing apparatus which utilizes a pair of tilted drive wheels of tapered shape for simultaneously imparting rotational and radial force to a workpiece.
Another object of the invention is to provide a surface finishing apparatus which utilizes speed follower control wherein the running speed of the drive wheels is inversely related to the operational speed of the surface finishing.
Another object of the invention is to provide a surface finishing apparatus which has a constant peripheral speed for board edges and thus avoids uneven application of decorative coating to board edges.
Another object of the invention is to provide a surface finishing apparatus which utilizes an air clamp for holding workpieces against the drive wheels.
Another object of the invention is to provide a surface finishing apparatus which may be used for edge foiling of wood boards or other workpieces having irregular, curvilinear and/or contoured edges. Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.